Method and apparatus for carrying out operations on a well under water



Jan. 14, 1969 J. VAN GEIJN 3,421,581

METHOD AND APPARATUS FOR CARRYING OUT OPERATIONS ON A WELL UNDER WATERSheet Filed Sept. 12, 1966 F l G.

l NVENTOR JACOB VAN GEIJN BYI H l'S AGENT J. VAN GEIJN Jan. 14, 19693,421,581 METHOD AND APPARATUS FOR CARRYING OUT OPERATIONS 7 ON 'A WELLUNDER WATER Z of 2 Sheet File d Sept. 12, 1966 w A 4 a my W 0 7 WE 3 D 49 1/ My 2 w LN r I .ll. IJ 5 4 O V 4 4 I A 8 vlllu/ 4 6 11: 7

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INVENTOR H IS AGENT United States Patent 3,421,581 METHOD AND APPARATUSFOR CARRYING OUT OPERATIONS ON A WELL UNDER WATER Jacob Van Geijn, TheHague, Netherlands, assignor to Shell Oil Company, New York, N.Y., acorporation of Delaware Filed Sept. 12, 1966, Ser. No. 578,831

Claims priority, application Great Britain, Oct. 19, 1965,

, 44,242/65 US. (:1. 166.5 9 Claims Int. Cl. E21b 33/035,- E21b 7/12,-E21b 43/01 ABSTRACT OF THE DISCLOSURE Method and apparatus for carryingout operations with respect to an underwater well wherein a pipe stringis secured between the well and a platform mounted on a floating vesselover the well site. The platform is mounted for vertical movementrelative to the vessel and is continuously biased in an upwardlydirection during said relative movement to maintain the drill pipe undertension and compensate for up and down movement of said vessel.

This invention relates to a method and to apparatus for carrying outoperations, for example, maintenance work, through a pipe string on anoilor gas well under water.

In deep water, floating structures are sometimes used, from whichoperations on an oilor gas well are carried out, but difficulty isexperienced if the floating structure tends to sway and to movevertically because of waves, since it is rather disturbing when it isnecessary to carry out from the structure operations on an oilor gaswell under water. It is an object of the invention to provide a methodand apparatus having the advantage that the influence of the sway and ofthe vertical movement of the floating structure is compensated for, sothat they no longer disturb the operations to be carried out.

The method according to the invention therefore comprises securing thepipe string to a subsea object such as the wellhead of a well, securingthe top part of the pipe string to a platform arranged on a floatingvessel which platform is so secured to the vessel that it is movablerelatively to the vessel, applying an upwardly directed force to theplatform so as to keep the pipe string under tension, and carrying outoperations on the well from the platform and through the pipe string.

A floating structure for carrying out the method according to theinvention comprises a platform so secured to a floating vessel that itis movable relative to the vessel, a vertical opening in the platform, aclamping device near the opening for securing a vertical pipe string tothe platform and means on the structure for applying an upwardlydirected force to the platform.

The invention may be carried into practice in various ways but twospecific embodiments will not be described by way of example withreference to the drawings in which:

FIGURE 1 is a diagrammatic side elevation of an em bodiment of afloating structure suitable for carrying out the method according to theinvention, and

FIGURE 2 shows a modified embodiment of a floating structure suitablefor carrying out the method according to the invention.

FIGURES 1 and 2 both show a floating structure 1 floating in a body ofwater 2 having a water level 3, which structure 1 comprises a vessel 4and a platform 5. The platform 5 is so secured to the floating vessel 4,for example by suitable vertical guide means (not shown), that it isvertically movable relatively to the vessel 4. A vertical opening 6 ispresent in the platform 5. Adjacent to Patented Jan. 14, 1969 theopening 6 is arranged a clamping device 7 which serves for securing avertical pipe string 8 to the platform 5. In the vessel 4 a verticalhole 9, which is for example cylindrical, is present to allow the pipestring 8 to pass through the vessel 4. Emergency controls must beprovided to stop the platform 5 from shooting upwardly in the event ofthe pipe string 8 breaking or becoming loosened. Before the pipe string8 is connected to a wellhead it must be possible to raise and lower theplatform 5 and only when the pipe string 8 has been connected to thewellhead will the platform 5 be allowed to exert an upward force on thepipe string 8.

The clamping device 7 is preferably removable, and can also be used toraise or lower pull out pipe strings between the structure and thewellhead. The vertical hole 9 should be large enough to permit liftingthrough hole 9 of Christmas trees, blow-out preventers or otherequipment. Furthermore, the hole 9 need not be cylindrical, but it maywiden from its upper to its lower ends.

In the embodiment shown in FIGURE 1 cables 10 are secured to theplatform 5, the other end of each cable 10 being provided with a weight11 and each cable 10 being led over a pllley 12. Each pulley 12 isrotatably secured to a piller 13 which is supported by the vessel 4.Each pulley 12 is arranged at a level above the highest possibleposition of the platform 5 relative to the vessel 4.

The floating structure as shown in FIGURE 1 is used as follows.

One end of at least one pipe string 8 is latched on to a subsea object,for example to an oil well (not shown), for example by using divers, orguiding cables, or a remotely operated propulsion device having atelevision camera. The pipe string 8 is connected with one end to thesubsea object by suitable connections, for example by connections whichcan be remotely operated and which may include emergency releases. Theupper end of the pipe string 8 is passed through the hole 9 and throughthe opening 6. By means of the clamping device 7 the upper end of thepipe string 8 is fixedly secured to the platform 5. The weights 11secured by the cables 10 to the platform 5 exert upwardly directedforces on the platform 5 and since the platform 5 is secured to the endof the pipe string 8, the latter will always be kept under tension. Ifthe vessel 4 moves vertically because of the waves, the platform 5 willremain in its position so that the vessel 4 will move verticallyrelatively to the platform 5. When the vessel 4 moves upwardly thepillars 13 and the pulleys 12 will move upwardly as well and since theplatform 5 remains stationary the pulleys 12 will be caused to rotateand the weights 11 will be displaced upwardly relatively to the platform5. When the vessel 4 moves downwardly the platform 5 will remainstationary and the pulleys 12 will be caused to rotate in the oppositedirection and the weights 11 will be displaced downwardly relatively tothe platform 5. From the above, it will be clear that, irrespective ofthe waves, the platform 5 will always remain at the same level and thatthe pipe string 8 will always be kept under tension.

From the platform 5 drillingor wireline operations can be carried out.The platform 5 can be provided with conventional equipment for carryingout wireline operations, for example equipment as shown in FIGURE 1 andindicated by the numbers 14, 15, 16, 17, 18, 19, 20, 21, 22. Since thisequipment does not form part of the invention it will not be discussedin detail.

The embodiment as shown in FIGURE 2 is provided with a hydraulic systemfor moving the platform 5 relatively to the vessel 4 instead of thesystem comprising weights 11 as shown in FIGURE 1. It is remarked,however, that instead of counterweights or a hydraulic system it is alsopossible to use a pneumatic or an electrical system, if desired. On thevessel 4 a number of (for example four) hydraulic cylinders 23 isarrange din each of which a plunger or piston (not shown) is presentwhich is axially movable in the cylinder 23. To each plunger or piston abar or rod 24 is secured, of which the upper end is connected to theplatform 5. The connection of the bars or rods 24 with the platform maybe direct or through a gimbal support. The axial (vertical) movement ofthe bars or rods 24 may be controlled by any suitable control systemwhich senses the deviation or any derivative of the deviation of theplatform from the desired horizontal plane. In the system as shown inFIGURE 2, the deviation of the platform from the desired horizontalplane is sensed by a sensing device 25. From the sensing device 25signals can be transmitted through a line 26 to a controller 27. Thetension in the pipe string 8 can be sensed by sensing devices 28 whichare each connected to one of the cylinders 23 by lines 29. Each sensingdevice 28 is connected to the controller 27 by lines 30 through whichsignals can be transmitted from the sensing devices 28 to the controller27. The controller 27 can process the signals, received from the sensingdevices 25 and 28, and can decide on the hydraulic pressures required inthe cylinders 23 to keep the platform 5 in the desired horizontal planeand to keep the pipe string 8 under the proper tension. The controller27 can then regulate the pressure in the cylinders 23 accordingly, e.g.by operating threeway control valves 31 and 32 by sending through lines35 signals to servo-valve mechanisms 33 and 34. The valves 31 and 32 arearranged respectively in a line 36 and in a line 37 which each connectthe pressure side of a liquid-pump 38 with a corresponding cylinder 23.The suction side of the pump 38 is connected through a line 39 to a tank40 containing a suitable liquid, for example oil. A drain line 41connects the valve 31 with the top of the tank 40 and a drain line 42connects the valve 32 to the drain line 41. By properly positioning thethreeway valves 31 and 32, liquid can be pumped from the tank 40 to thecylinder 23 and/or be drained from the cylinders 23 so that the properpressure will be obtained in each of the cylinders 23. By means of thehydraulic system as described above the platform 5 will, irrespective ofthe waves, always remain in the desired horizontal plane and the pipestring 8 will always be kept under tension.

On the platform 5 can be located conventional equipment for carrying outdrilling operations, for example a derrick 43, a hoist 44, a cable 45, atravelling block 46 (shown in FIGURE 2) for lowering the pipe string 8or hoisting the pipe string 8 from the hole 9 or for lowering pipes 48into or hoisting pipes 48 from the pipe string 8.

It is to be noted that instead of the counterweights or the hydraulicsystem as described it is possible to use a pneumatic or electricsystem. It is for example possible to keep the pressure in each cylinder23 substantially constant in all positions of the platform 5 byconnecting each cylinder 23 to a corresponding pressure tank (notshown), containing gas and having a volume which is large relative tothe volume of the corresponding cylinder 23.

Furthermore attention is drawn to the fact that instead of one pipestring 8 as shown, it is possible to use a plurality of pipe stringswhich are parallelly or concentrically arranged.

I claim as my invention:

1. A method of carrying out operations, for example maintenance work, ona well under water through a pipe string, comprising securing the pipestring to a subsea wellhead of a well, securing the top part of the pipestring to a platform, arranging said platform on a floating vessel in amanner such that the platform is vertically movable relatively to thevessel, applying an upwardly directed force to the platform with saidforce independent of the motion of said vessel so as to keep the pipestring under tension, and carrying out operations on the Well from theplatform and through the pipe string.

2. The method as claimed in claim 1, wherein the upward force acting onthe platform is created by means of a weight.

3. The method as claimed in claim 1, in which the upward force acting onthe platform is created by a piston arranged in a fluid cylinder.

4. A floating structure for carrying out operations at offshorelocations, said structure comprising a platform so secured to a floatingvessel that it is vertically movable relatively to the vessel, avertical opening in the platform, a clamping device near the opening forsecuring a vertical pipe string to the platform and means on thestructure for applying an upwardly directed force to the platform assaid platform moves vertically relative to said vessel.

5. The structure as claimed in claim 4, in which the means for applyingan upwardly directed force to the platform comprise a cable having oneend secured to the platform and the other end to a weight, the cablebeing led over a pulley which is arranged on the structure at a levelabove the highest position of the platform relatively to the vessel.

6. The structure as claimed in claim 4, in which the means for applyingan upwardly directed force to the platform comprise a cylinder arrangedon the structure, a piston arranged in the cylinder, a connectionbetween the piston and the platform, and fluid under pressure in thecylinder.

7. The structure as claimed in claim 6, in which means are present forcontrolling the pressure in the cylinder.

8. The structure as claimed in claim 6, in which a system is present forkeeping the pressure in the cylinder substantially constant in allpositions of the platform relatively to the vessel.

9. The structure as claimed in claim 8, in which the system for keepingthe pressure in the cylinder constant comprises a pressure tankcontaining gas and having a volume which is large relative to the volumeof the cylinder, and a fluid connection between the cylinder and thepressure tank.

References Cited UNITED STATES PATENTS 2,181,641 11/1939 Hicks -220 X3,110,350 11/1963 Spiri 1755 3,177,954 4/1965 Rand 166.6 X 3,179,1794/1965 Kofahl 166.5 3,195,639 7/1965 Pollard et a1 1757 X 3,221,81712/1965 De Vries et a1. 166.5

CHARLES E. OCONNELL, Primary Examiner.

R. E. FAVREAU, Assistant Examiner.

US. Cl. X.R. 1755, 27

